1. Field of the Invention
This invention relates to syringes for collecting blood samples, and more particularly syringes of the type that are assisted in drawing blood by a vacuum in the interior of the syringe.
2. Description of the Prior Art
Syringe type devices are typically used for obtaining blood samples to perform a blood gas analysis. In these tests it is important that air and other materials contained in anti-coagulant solutions, such as water which is a diluent for the heparin, are not allowed to contaminate the blood and distort the results of the gas analysis. Several syringe devices have been developed to obtain contaminant free blood samples. Examples of such syringe devices are disclosed in my pending U.S. patent application for a Syringe Device With Means for Selectively Isolating a Blood Sample After Removal of Contaminates and Method of Using Same, Ser. No. 952,994, filed Oct. 20, 1978 and in U.S. Pat. Nos. 3,978,846 and 4,133,304 of which I am also the inventor.
However, not all individuals have a blood pressure which is high enough to fill the body of a syringe to a preselected volume necessary to conduct blood gas analysis. This is particularly true with small babies, especially premature babies, whose blood pressure is so low that it is difficult to get any flow whatsoever into a conventional syringe device. The newborn or premature baby problem is further complicated by the size of the arteries and veins and incumbent restrictions on the gauge of the needle that must be used to penetrate the artery or vein. The small dimensions, necessarily encountered, of the needle, impede any blood flow that might be expected.
In obtaining blood samples it is necessary to use an anti-coagulant to maintain the integrity of the blood sample. Typically, a dilute heparin solution of 1,000 units per milliliter in alcohol and water has been placed within the syringe body prior to use, which, after evaporation, leaves a deposit of heparin within the syringe body. This process takes a period of time, as long as an hour, and thus, undesirably extends the manufacturing time of the syringe when the syringe is provided with the dried heparin coating therein.